DB is not defined in configuration

I have a problem with my DAAB. I configured it in ent lib configuration tool, i checked the Connection string in app.config, and everything seems fine. But, when i try to start the application, the error occurs and it says :

"The requested database is not defined in configuration"

I don't have any other configuration files rather than app.config, would that be a problem, and I don't know how to create dataConfiguration.config if it is necessary... Could anyone help me please ? I'm sooo stucked with this!!!

It is not necessary to create a separate dataConfiguration.config. Did you add the connection strings under the Data Access Application block in your config? Please post your <dataConfiguration> section and your call to DatabaseFactory.CreateDatabase
here.

Are you getting the same error? (The requested database is not defined in configuration). How about the null reference exception? From what line of code are you encountering it? Is that code part of an executable project or a class library?

I think you should be defining the connection string to the app.config of the application hosting the class library. Example, if a Console Application is using your class library, you should define the connection string to the app.config of the console
application.